Fish was asked by Lord Rothschild to draw his impression of what such a package may look like based on its few known features.

Lord Rothschild's letter in full

"When you break off a piece of chocolate at one end in the normal way, instead of it falling away, a piece of canvas is revealed stuck into the middle of the piece which has been broken off and a ticking into the middle of the remainder of the slab," Rothschild explained.